The use of and demand for offshore platforms has grown tremendously in recent years as the demand for new oil and gas supplies has increased. To meet the demand for platforms in different environmental conditions, many different structures and fabrication methods have been proposed and used; and each new generation of structures has generally provided greater stability and safety.
Stability and safety in offshore platforms has not come cheaply however. In efforts to reduce the cost of offshore installations, there have been proposed various types of mobile platforms, platform assemblies which may be moved, either under their own power or under tow, to an offshore installation site. There, the offshore platform is installed, used, and at the end of its utility at the site, may be refloated and moved to a new site. Thus the capital cost of the platform may be spread over several sites.
While mobile offshore platforms have been considered by some as the way of the future in many applications, their design has been in but the preliminary stages. Thus, many previously proposed mobile platforms have a platform or deck structure which is of limited usefulness because of obstructions in the work area. The obstructions are generally associated with the equipment required to raise and/or lower the deck relative to a stable gravity base unit. The base rests on the seabed in normal operation. Other units are either difficult to construct or are overly expensive; and yet other units do not provide the stability necessary for many applications.
Additionally, existing mobile platforms, which may be floated to the site, have generally not been useful at depths below 250-350 feet. Therefore, as the need to venture into deeper waters continues to grow, the mobile platform has not heretofore been considered a viable alternative and thus the more expensive fixed platform must be used or adapted to the greater depths.
It is therefore an object of the invention to provide mobile offshore platform assemblies and methods of fabrication which are relatively inexpensive, have improved stability, and are capable of operating at from shallow depths up to depths of 1500 feet or more. Other objects of the invention include providing a mobile offshore platform assembly wherein the assembly may be fabricated onshore and floated to the installation site, wherein derrick barges are not required to install the platform assembly and wherein the means for spacing the deck portion of the assembly relative to the base portion of the assembly are commercially available and are reuseable from one installation site to another.
Other objects of the invention include a base member which can be used for oil storage, a platform assembly which can be salvaged and reused, and an assembly wherein operations can be commenced very quickly after base grouting has been completed.
Still other objects of the invention are a platform design wherein the various components of the platform assembly can be highly standardized and optimized, and wherein quality control during fabrication of the platform can be greatly increased by producing the components under controlled conditions.
Yet another object of the invention is to provide a platform assembly which can be equipped and tested prior to being towed to the installation site.
Still another object of the invention is to provide a platform assembly wherein the load is substantially uniformly distributed throughout the base member.